A "drill bit" is defined as a removable drilling or boring tool for use in a brace, drill press, or the like, and will generally be of a type that is classified either as an auger or as a straight shank drill bit. Of particular interest for the present invention is the so-called straight shank drill bit.
In order to drill or bore a hole into a surface with a straight shank drill bit, the drill bit is rotated relative to the surface by a brace or drill press. Sharp edges on the front or tip of the drill bit then cut into the surface. Due to the drill bit's configuration, the material that is cut as the drill bit is rotated is removed so that the result is a clean hole in the surface. Not surprisingly, with extended use, a drill bit can become worn. Thus, periodic screening may be necessary to determine whether the drill bit can be reshaped and reused, or must be discarded. Whenever a large number of particularly small drill bits are involved, the inspection and selection process for screening the drill bits can become quite labor intensive and very time consuming.
It happens that there is a standard configuration for straight shank drill bits. Importantly, although the particular dimensions of drill bits and the exact angles between respective component parts of different drill bits will vary, all straight shank drill bits generally have the same general configuration. Consequently, the component parts of the drill bit always have the same relationship relative to each, and they always have the same relationship relative to the longitudinal axis of the drill bit. Specifically, at the front end, or tip, of the drill bit are a pair of component parts more commonly referred to as primary facets. These primary facets are generally flat surfaces, and they each have a side which is aligned along a common diameter (extension line). Further, the primary facets are on opposite sides of the drill bit's longitudinal axis, and they are on opposite sides of their common diameter (extension line). Depending on the model of the drill bit, a normal to the primary facets will be inclined to the longitudinal axis of the drill bit by an angle .alpha..
In addition to the primary facets mentioned above, the tip of the drill bit is also formed with a pair of diametrically opposed secondary facets that are each juxtaposed with a respective primary facet. Additionally, the drill bit has a pair of helical shaped flutes that continue from a respective secondary facet and extend generally along the length of the drill bit shank parallel to the axis. Each of these flutes is characterized by a margin that borders the flute along the length of the drill bit. For operational purposes, however, of all the component parts of the drill bit, it is the primary facets that face the most wear and are, therefore, of most concern. As indicated above, however, the primary facets are positioned in a rather complex geometrical orientation on the drill bit. Accordingly, any regrinding of the primary facets that may be necessary in order to maintain the serviceability of the drill bit must be done with a great deal of precision and care.
There are many optical techniques which have been used for purposes of inspecting and evaluating various items. While some of these techniques merely require adequate illumination of the item, others can involve highly sophisticated interference, absorption or specular analysis. In each case, some aspect or characteristic of light plays an important role. For the present invention, the characteristic of light that is of most importance is reflection.
In general, the reflection of light from an object can be classed as being either specular reflection or non-specular, diffuse reflection. In the case of non-specular or diffuse reflection, the reflection of light from a rough surface results in a scattering of the light wave components. On the other hand, the specular reflection of light occurs when a wavefront of light is diverted from a polished surface, so that the angle of the incident wave to the normal at the point of reflection is the same as that of the reflected wave. For irregular shaped objects, such as a drill bit, the specular reflection of light can be observed from predetermined surfaces. Specifically, depending on the known location of a light source, and the expected location of a particular surface, a detector (such as a camera) can be appropriately positioned to receive a specular reflection from the surface. The presence or absence of the specular reflection can then be used as intelligence for purposes of orienting or inspecting the item on which the surface is located.
In light of the above, it is an object of the present invention to provide an optical device and a method which uses specular reflections from a drill bit to establish a spatial orientation for the drill bit. Another object of the present invention is to provide an optical device and a method which uses specular reflections from a drill bit, in concert with other illumination techniques, to measure dimensions of the drill bit. Still another object of the present invention is to provide an optical device and a method which uses specular reflections to inspect for irregularities in selected surfaces and boundaries of these surfaces. Yet another object of the present invention is to provide an optical device and a method which is easy to use, relatively simple to manufacture, and comparatively cost effective.